This research study is a Phase I clinical trial, which tests the safety of an investigational combination of IL-2 plus donor anti-inflammatory Treg cells and also tries to define the appropriate dose of the investigational combination of IL-2 plus donor anti-inflammatory Treg cells to use for further studies. IL-2 is involved with cell signaling and regulation of white blood cells (WBCs). WBCs are part of the immune system. Treg cells are also part of the immune system; they are involved with anti-inflammatory responses. "Investigational" means that the combination of IL-2 and anti-inflammatory Treg cell infusion is being studied. It also means that the FDA (U.S. Food and Drug Administration) has not approved the combination of IL-2 and anti-inflammatory Treg cell infusion for use in people with cGVHD.